Lib Dem leader Vince Cable. ‘There are many explanations for the Lib Dems’ current predicament, but at their conference next week the party must not wallow in excuses.’ Photograph: Dan Kitwood/Dan Kitwood

One side-effect of the ideological mania gripping the Conservatives is to put a retrospective gloss on the 2010-15 coalition government. There is not much to cherish in the legacy of the administration that set Britain on an ill-judged course of austerity. But the unleashing of a more fanatical rightwing Tory impulse since 2015 testifies, in hindsight, to the restraining, if limited, influence of the Liberal Democrats in government. That isn’t much use to Vince Cable, a coalition cabinet minister three years ago, now leading a party parked on the margins. A reconfiguration of British politics – with Jeremy Corbyn’s Labour moving leftward and a radical rightwing Tory agenda – ought, perhaps, to leave room for a third-way English party. Yet the Lib Dems haven’t expanded into the space.

Their desultory performance has many causes. To protest against New Labour governments from a liberal-left position, only to then join forces with the Conservatives, was too violent a lurch for many of the party’s natural supporters. It looked craven in pursuit of power and the brand never recovered. Britain’s electoral system doesn’t help, squeezing smaller parties. The Lib Dems find themselves defined more by what they are not (neither Labour nor Tory) than by what they are. To articulate a positive identity will be Mr Cable’s most challenging task at his party’s annual conference next week. It should be added that the task is the same one that faced his predecessors, Tim Farron and Nick Clegg. When a mission goes unaccomplished for so long the question arises as to whether it can be done at all. The Lib Dems have been written off in the past and recovered. They are a resilient bunch, but no party has an inalienable right to be relevant.

Mr Cable does grasp the seriousness of the predicament. He has proposed substantial reforms to the party’s structure: opening it up to loosely affiliated supporters, making it easier for rank-and-file members to be selected as parliamentary candidates, making the leadership available to those outside parliament. In this way Mr Cable hopes to infuse his organisation with new energy in tune with the insurgent spirit of the times. He wants the Lib Dems to be a “movement for moderates”.

That might be a contradiction in terms. Traditionally, the moderate middle-way voter has not easily been fired up for activism in the way that movement politics implies. Much of the appeal of incremental, technocratic politics is that it leaves most citizens free to get on with their lives. But Mr Cable’s contention is that the current moment is different, chiefly because of Brexit, and that the liberal centre is ready to rise up. He may be right, although there is a catch: resistance to Brexit gives the Lib Dems a distinctive position, but it also risks orienting them towards the past and nostalgia for a less febrile era. That is not the insurgent style. That may be Mr Cable’s problem. He makes a good commentator on what ails the nation, but commentary and leadership are different skills.

The Lib Dems have faced structural obstacles to success in a polarised political climate, but when Brexit is such a conspicuous shambles it should have been possible, with some campaigning zeal, for the small, unabashedly pro-European party to raise its profile. That it has failed suggests a lack of urgency and dynamism at the top. There are many explanations for the Lib Dems’ current predicament, but at their conference next week the party must not wallow in excuses. The opportunity for a revival is real, and there is a real risk that it is being squandered.